The present invention generally relates to crankshafts for small reciprocating machines, such as engines and compressors and, more particularly, to such a crankshaft fabricated from more than one material.
Crankshafts have conventionally been cast or forged in a single piece. However, the complex shape of many crankshafts makes such manufacture relatively costly. Therefore, it has been found that production costs can be reduced by separately manufacturing the elements or segments forming the crankshaft and then assembling the segments together. For example, it is known to manufacture a crankcase by forging two separate segments and joining them together by a welding technique such as friction welding. In addition, it has been found that costs can be further reduced by manufacturing the individual crankshaft elements from different materials. For example, in one prior art crankshaft, the element comprising the eccentric and crankpin is formed of sintered metal, and the elongate tubular part of the crankshaft is formed of low-cost soft steel such as "Fe 35". The two elements are then joined together by projection welding to form the crankshaft. The use of less costly material for the segments of the crankshaft that are subject to reduced stresses decreases the overall cost of production.
It is desired to provide a crankshaft that lends itself to extremely economical manufacture.